1. Field of the Invention
The present invention relates to an elevator car safety device. More particularly, the invention relates to an elevator car safety system which is operative to restrain movement of the car when the car doors are open.
2. Description of the Prior Art
Elevator systems of the prior art typically include an elevator car connected to a counterweight by means of a steel cable which is adapted to extend over a sheave located in the machine room located at the top of an associated elevator shaft. The sheave is connected to a hoist motor provided to effect vertical movement of the elevator car in the elevator shaft.
The hoist motor, provided with a brake, is connected to the sheave to control the rotation of the sheave and thus the vertical motion imparted to the elevator car. The brake is directly connected to the sheave and is employed to hold the elevator car in a stationary position.
The system further includes a safety governor which includes a governor rope which passes over a safety governor pulley located in the machine room and then extends downwardly to a tensioning pulley located at the bottom of the elevator shaft and then extends back to the governor pulley. The governor rope is typically connected to a progressive safety mounted in the elevator car. The safety governor is adapted to detect an overspeed condition of the elevator car based upon a ratio of the rotational velocity of the governor pulley proportional to the speed of the elevator car.
Safety governors are known in the prior art such as the governor illustrated and described in U.S. Pat. No. 4,556,155. The governor is provided with two diametrically opposed flyweights disposed on the governor pulley. In operation, as the elevator car travels up and down the elevator shaft, the flyweights move outwardly due to the centrifugal force imparted thereon by the rotating governor pulley.
When the speed of the elevator car exceeds a rated speed by a predetermined value, the flyweights are driven outwardly and are caused to trip an overspeed switch which cuts off power to the drive motor and simultaneously sets the brake.
In the event the elevator car speed continues to increase, the further outward motion of the flyweights causes the flyweights to contact and trip a mechanical latching device, releasing a swinging jaw which is normally held away from the governor rope. When the swinging jaw is released, it clamps the governor rope against a fixed jaw, thereby retarding governor rope motion. The retarding action exerted on the governor rope causes safeties located on the elevator car to engage, thereby progressively decelerating and ultimately arresting the motion of the elevator car.
There are a number of safeties known in the prior art, such as, for example, a safety having a roller located between the elevator car guide rail and a leaf spring. The leaf spring and the guide rail form a triangular section with the roller located at the base of the triangular section during normal operation.
The force exerted on the governor rope causes a safety gear linkage to lift the roller into the tapered portion of the triangular section. The leaf spring exerts pressure on the guide rail by way of the roller, and the pressure is progressively increased as the roller moves into the tapered portion of the triangular section. The executed pressure gradually decelerates and ultimately arrests the motion of the elevator car.
In operation, an elevator car is dispatched to a floor in response to a hall call and/or a car call. For the sake of efficiency, it is desirable to have the elevator car door begin to open prior to the car coming to a complete stop at the floor landing. Safety codes permit the elevator car door to commence opening prior to the elevator car coming to a complete stop. The codes permit such operation if the elevator car is within a predetermined zone, commonly referred to as an outer door zone, and a further proviso that the elevator car is travelling below a predetermined speed. The outer door zone is typically defined as a zone twenty-four (24) inches centered about the floor landing.
The arriving elevator car decelerates and, upon reaching the outer door zone, commences opening the car door. The elevator car will hover at the landing until it is level with the landing. When the elevator car is properly positioned at the landing, the brake is set and the drive motor is de-energized. In the event the elevator car should drift from the landing, the drive motor is caused to be re-energized to cause the car to be moved to the proper landing level.
Normally, an engaged drive and a set brake are each capable of holding the elevator car at the landing and/or stationary. However, in the event the drive or the brake should malfunction, the elevator car can drift away from the landing.
Other approaches to solve the problem include the use of electronic circuitry to monitor the speed of the elevator car, the position of the elevator car, and the state of the elevator car door. Once these parameters are within a certain predetermined range, a rope or cable brake is activated or an independent machine brake is activated.
Safety codes are being promulgated to require that a drifting elevator car should be stopped should the elevator car drift more than twenty (20) inches from a landing with the door in an open position. More specifically, the codes provide that if an elevator car drifts more than twenty (20) inches from a landing with the door open, the elevator car must be brought to a complete stop within another thirty (30) inches.
It is an object of the present invention to produce a safety system which will prevent further movement of the elevator car should the car drift beyond a predetermined distance with the door in an open position.